Process for drawing polybenzimidazole fibrous materials

ABSTRACT

DRAWING   1. AN IMPROVED CONTINUOUS PROCESS FOR THE HOT DRAWING OF A CONTINUOUS LENGTH OF A POLYBENZIMIIDAZOLE FIBROUS MATERIAL CONTAINING UP TO ABOUT 100 PERCENT BY WEIGHT OF WATER, SAID DRAWING OCCURING WITHOUT FOAMING AND WITHOUT WEMPOLYING MULTIPLE PASSES OF THE FIBROUS MATERIAL THROUGH THE DRAWING ZONE OF DRAWING THE FIBROUS MATERIAL WHILE IN CONTACT WITH A HEATED SURFACE, WHICH PROCESS COMPRISES: (A) CONTINUOUSLY PASSING SAID CONTINUOUS LENGTH OF POLYBENZIMIDAZOLE FIBROUS MATERIAL IN THE DIRECTION OF ITS LENGTH, FOR A SINGLE PASS, THROUGH AN ELONGATED DRAWING ZONE CONTAINING A HEATED GASEOUS ATMOSPHERE MAINTAINED AT A TEMPERATURE OF ABOUT 400 TO 600*C., (B) CONTINUOUSLY PASSING A PREHEATED GAS INTO SAID DRAWING ZONE AT A RATE WHICH YIELDS A REYNOLD&#39;&#39;S NUMBER WITHIN THE DRAWING ZONE OF ABOUT 50 TO 50,000 SO AS TO CONTACT SAID FIBROUS MATERIAL THEREIN, (C) DRAWING SAID FIBROUS MATERIAL IN SAID DRAWING ZONEWHILE IN CONTACT WITH SAID REPHEATED GAS AT A DRAWRATIO OF ABOUT 2:1 TO 5:1 AND AT A DRAWING SPEED OF AT LEAST 10 METERS PER MINUTE, AND (D) THEREAFTER CONTINUOUSLY WITHDRAWING FROM SAID DRAWING ZONE A STREAM OF GAS AND DRAWN POLYBENZIMIDAZOLE FIBROUS MATERIAL.

Nav. 19, 1974 Q R, FERMENT ETAL 3,849,529

PROCESS lFOR DRAWING POLYBENZIMIDAZOLE FIBRous MATERIALS Filed Oct. 13,1972 nted States Patent O Filed Oct. 13, 1972, Ser. No. 297,511 Int. Cl.B29c 17/02; D02j 1/22 U.S. Cl. 264-85 8 Claims ABSTRACT OF THEDISCLOSURE An improved process is provided for the hot drawing of acontinuous length of a polybenzimidazole fibrous material on acontinuous basis, without foaming, in a single pass. The fibrousmaterial is drawn while suspended in an elongated drawing zone providedwith a owing heated gaseous atmosphere wherein heat radiantly issupplied to the fibrous material from the walls of the drawing zone aswell as by contact with a stream of preheated gas (aS defined). Thefibrous material may optionally be supplied to the drawing zone while inassociation with a substantial quantity of water thereby eliminating thenecessity to carry out a conventional drying step prior to hot drawing.

BACKGROUND OF THE INVENTION Heretofore continuous lengths ofpolybenzimidazole fibrous materials have been hot drawn (1) while insliding contact with a hot surface, eg., a hot shoe, or (2.) whilepassing for a plurality of passes through a radiantly heated drawingzone in which the fibrous material is suspended. When employing eitherprior art drawing technique, it has been essential that thepolybenzimidazole fibrous material be dried and substantially free ofwater prior to introduction into the drawing zone if optimum tensileproperties are to be achieved. Diliiculties have been encountered withhot shoe polybenzimidazole drawing techniques because of solid depositformation upon the hot contact surface which requires periodic cleaning,and which may result in fiber damage and decreased line stability ifallowed to accumulate. Also, precise hot shoe temperature maintenanceuniformity has been of prime importance. When radiant heat has beensupplied to the polybenzimidazole fibrous material in prior arttechniques (e.g., the process of U.S. Pat. No. 3,622,660), it has beenessential that the continuous length of fibrous material be passedthrough the drawing zone for a plurality of passes in order toaccomplish the desired degree of drawing. Such processes additionallyrequire a complex string-up arrangement which is impractical for largescale economic production, and commonly are accompanied by theproduction of broken filaments.

It is an object of the present invention to provide an improvedcontinuous hot drawing process for a continuous length of apolybenzimidazole fibrous material.

It is a object of the present invention to provide an irnprovedcontinuous hot drawing process for a continuous length of apolybenzimidazole fibrous material which eiiciently is carried out on astable 'basis upon a single pass through a hot drawing zone.

It is an object of the present invention to provide an improvedcontinuous hot drawing process for a polybenzimidazole fibrous materialwherein the fibrous material fed to the drawing zone optionally may bein association with a substantial quantity of water.

`It is an object of the present invention to provide an irnprovedcontinuous hot drawing process for a polybenzimidazole fibrous materialwhich is conducted in the absence of contact with a hot draw surface,e.g., a hot shoe, or pin.

ice

It is a further object of the present invention to provide an improvedcontinuous hot drawing process for a polybenzimidazole fibrous materialwhich is capable of yielding a product of superior fiber uniformity.

It is a further object of the present invention to provide an improvedcontinuous hot drawing process for a polybenzimidazole fibrous materialwhich is not unduly sensitive to the maintenance of a narrowly defineddrawing temperature.

These and other objects, as well as the scope, nature, and utilizationof the process will be apparent from the following detailed descriptionand appended claims.

l SUMMARY OF THE INVENTION It has been found that in a continuousprocess for the hot drawing of a continuous length of apolybenzimidazole fibrous material at a draw ratio of about 2:1 to 5:1and at a drawing speed of at least l0 meters per minute improved resultsare achieved by:

(a) Continuously passing the continuous length of polybenzimidazolefibrous material in the direction of its length while under alongitudinal tension for a single pass through an elongated drawing zonewherein the drawing is accomplished which is provided with a heatedgaseous atmosphere at a temperature of about 400 to 600 C. in which thefibrous material is suspended and in which radiant heat is supplied tothe fibrous material from the walls of the drawing zone,

(b) Continuously introducing into the gaseous atmosphere of theelongated drawing zone at least one stream of preheated gas whichimpinges upon the moving continuous length of polybenzimidazole fibrousmaterial within the elongated drawing zone and flows within theelongated drawing zone, and

(c) Continuously withdrawing from the gaseous atmosphere of theelongated drawing zone at least one stream of gas.

DESCRIPTION OF THE DRAWINGS FIG. l is a schematic illustration of anapparatus capable of carrying out the improved continuous hot drawingprocess of the present invention.

FIG. 2 is a schematic illustration of an additional apparatus capable ofcarrying out the improved continuous hot drawing process of the presentinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS The Starting PolymerPolybenzimidazoles are a known class of heterocyclic polymers. Typicalpolymers of this class and their preparation are more fully described inU.S. Pat. No. 2,895,948, U.S. Re. Pat. No. 26,065, and in the Journal ofPolymer Science, vol. 50, pp. S11-539 (1961) which are hereinincorporated by reference. The polybenzimidazoles consist essentially ofrecurring units of the following Formulas I and II. Formula I is:

wherein R is a tetravalent aromatic nucleus, preferably symmetricallysubstituted, with the nitrogen atoms forming the benzimidazole ringsbeing paired upon adjacent carbon atoms, i.e., ortho carbon atoms, ofthe aromatic nucleus, and R is a member of the class consisting of l) anaromatic ring, (2) an alkylene group (preferably those having 4 to 8carbon atoms), and (3) a heterocyclic ring from the class consisting of(a) pyridine, (b) pyrazine,

(c) furan, (d) quinoline, (c) thiophen, (f) pyran.

Formula II is:

wherein Z is an aromatic nucleus having the nitrogen atoms forming thebenzimidazole ring paired upon adjacent carbon atoms of the aromaticnucleus.

Preferably, aromatic polybenzimidazoles are selected, e.g., polymersconsisting essentially of the recurring units of Formulas I and IIwherein R is an aromatic ring or a heterocyclic ring.

As set forth in U.S. Re. Pat. No. 26,065, the aromaticpolybenzimidazoles having the recurring units of Formula II may beprepared by self-condensing a trifunctional aromatic compound containingonly a single set of ortho disposed diamino substituents and anaromatic, preferably phenyl, carboxylate ester substituent. Exemplary ofpolymers of this type is poly-2,5(6)benzimidazole prepared by theautocondensation of phenyl-3,4-diaminobenzoate.

As also set forth in the above-mentioned patent, the aromaticpolybenzimidazoles having the recurring units of Formula I may beprepared by condensing an aromatic tetraamine compound containing a pairof orthodiamino substituents on the aromatic nucleus with a dicarboxylcompound selected from the class consisting of (a) the diphenyl ester ofan aromatic dicarboxylic acid, (b) the diphenyl ester of a heterocyclicdicarboxylic acid wherein the carboxyl groups are substituents upon acarbon in a ring compound selected from the class consisting ofpyridine, pyrazine, furan, quinoline, thiophene and pyran and (c) ananhydride of an aromatic dicarboxylic acid.

Examples of polybenzimidazoles which have the recurring structure ofFormula I are as follows:

where the double bonds of the ethylene groups are intact in the finalpolymer.

The preferred polybenzimidazole for use in the present process is oneprepared from poly-2,2(mphenylene)- 5,5-bibenzimidazole, the recurringunit of which is:

fr @i .l

L \N yt@ With respect to aromatic polybenzimidazoles, preferablyequimolar quantities of the monomeric tetraamine and dicarboxyl compoundare introduced into a first stage melt polymerization reaction zone andheated therein at a temperature above about 200 C., preferably at least250 C., and more preferably from about 270 to 300 C. The reaction isconducted in a substantially oxygen-free atmosphere, i.e., below about20 p.p.m. oxygen and preferably below about 8 p.p.m. oxygen, until afoamed prepolymer is formed having an inherent viscosity, expressed asdeciliters per gram, of at least 0.1, and preferably from about 0.13 to0.3, the inherent viscosity (IV.) as used herein being determined from asolution of 0.4 grams of the polymer in ml. of 97 percent H2SO4 at 25 C.

After the conclusion of the first stage reaction, which normally takesat least 0.5 hour and preferably 1 to 3 hours, the foamed prepolymer iscooled and then powdered or pulverized in any convenient manner. Theresulting prepolymer powder is then introduced into a second stagepolymerization reaction zone wherein it is heated under substantiallyoxygen-free conditions, as described above, to yield a polybenzimidazolepolymer product, desirably having an LV., as measured above, of at least0.6, e.g., 0.80 to 1.1 or more.

The temperature employed in the second stage is at least 250 C.,preferably at least 325 C., and more preferably from about 350 to 425 C.The second stage reaction generally takes at least 0.5 hour, andpreferably from about 1 to 4 hours or more.

A particularly preferred method for preparing the polybenzimidazole isdisclosed in the aforesaid U.S. Pat. No. 3,509,108. As disclosed thereinaromatic polybenzimidazoles may be prepared by initially reacting themonomer in a melt phase polymerization at a temperature above about 200C. and a pressure above 50 p.s.i. (e.g., 300 to 600 p.s.i.) and thenheating the resulting reaction product in a solid state polymerizationat a temperature above about 300 C. (e.g., 350 to 500 C.) to yield thefinal product.

Preparation of the Continuous Length of Pibrous Material The termcontinuous length of polybenzimidazole fibrous material as used hereinincludes monofilaments, as Well as multifilament fibrous materials, suchas yarn,

' strand, cable, tow, and the like. In a preferred embodiment of theprocess the continuous length of polybenzimidazole fibrous material is amultifilament yarn or a multifilament tow.

As is known in the art, polybenzimidazoles are generally formed intocontinuous lengths of fibrous materials by solution spinning, that is,by dry or Wet spinning a solution of the polymer in an appropriatesolvent such as N, N-dimethylacetamide, N,Ndimethylformamide,dimethylsulfoxide or sulfuric acid (used only in wet spinning) throughan opening of predetermined shape into an evaporative atmosphere for thesolvent in which most of the solvent is evaporated (dry) or into acoagulation bath (wet), resulting in the polymer having the desiredfilamentary shape.

The polymer solutions may be prepared in accordance with knownprocedures, For example, sufficient polybenzimidazole may be dissolvedin the solvent to yield a final solution suitable for extrusioncontaining from about 10 to 45 percent by weight of the polymer, basedon the total weight of the solution, preferably from about 20 to 30percent by weight.

One suitable means for dissolving the polymer in the solvent is bymixing the materials at a temperature above the atmospheric boilingpoint of the solvent, for example 25 to 120 C. above such boiling point,and at a pressure of 2 to 15 atmospheres for a period of l to 5 hours.

Preferably, the polymer solutions, after suitable filtration to removeany undissolved portions, are dry spun. For example, the solutions maybe extruded through a spinneret into a conventional type downdraftspinning column containing a circulating inert gas such as nitrogen,noble gases, combustion gases or superheated steam. Conveniently, thespinneret face is at a temperature offrom about 100 to 170 C., the topof the column from about 120 to 220 C., the middle of the column fromabout 140 to 250 C., and the bottom of the column from about 160 to 320C. After leaving the spinning column, the continuous filamentarymaterials are taken up, for example, at a speed within the range ofabout 50 to 350 meters or more per minute. If the continuous filamentarymaterials are to be washed while wound on bobbins, the resulting asspunmaterials may be subjected to a slight steam drawing treatment at a drawratio of from about 1.05 :1 to 1.5 :1 in order to prevent the fibersfrom relaxing and falling off the bobbin during the subsequent washingstep. Further details with respect to a method for dry-spinning acontinuous length of a polybenzimidazole fibrous material are shown inU.S. Pat. No. 3,502,576 to Bohrer et al. which is assigned to the sameassignee as the present invention and is herein incorporated byreference.

The continuous length of polybenzimidazole fibrous material is nextwashed so as to remove at least the major portion of residual spinningsolvent, e.g., so that the washed materials contain less than about 1percent by Weight solvent based on the weight of the continuousfilamentary material, and preferably so as to obtain an essentiallyspinning solvent-free fibrous material (i.e., a fibrous materialcontaining less than about 0.1 percent solvent by weight). Typically, asimple water wash is employed; however, if desired, other wash materialssuch as acetone, methanol, methylethyl ketone and similarsolvent-miscible and volatile organic solvents may be used in place ofor in combination with the water. The washing operation may be conductedby collecting the polybenzimidazole fibrous material on perforated rollsor bobbins, immersing the rolls in the liquid wash bath and pressurewashing the fibrous material, for example, for about 2 to 48 hours ormore. Alternatively, the continuous length of polybenzimidazole fibrousmaterial may be washed on a continuous basis by passing the fibrousmaterial in the direction of its length through one or more liquid washbaths (e.g., for 1 to l0 minutes). Any wash technique known to thoseskilled in the art may be selected.

The continuous length of polybenzimidazole fibrous material may next bedried to remove the liquid wash bath by any convenient technique. Forinstance, the drying operation for bobbins of yarn may be conducted at atemperature of about 150 to 300 C. for about 2 to 100 hours or more.Alternatively, the continuous length of polybenzimidazole fibrousmaterial may be dried on a continuous basis by passing the fibrousmaterial in the direction of its length through an appropriate dryingzone (e.g., an oven provided at 300 to 400 C. for 1 to 2 minutes). Ifdrying is employed, preferably the drying temperature does not exceedabout 250 C. for several hours or 400 C. for more than one minute, asabove these limits degradation of the 'fiber may occur. The fibrousmaterial may be introduced into the drawing zone (described hereafter)while in a substantially anhydrous form immediately after drying (i.e.,may contain less than about 2 percent water based upon the weight of thefibrous material). As is known to those skilled in polybenzimidazolefiber technology, the fibrous material has a propensity to pick up about10 to 13 percent moisture by weight when exposed to ambient conditionsfor an appreciable period of time.

It is possible, however, that the continuous length of polybenzimidazolefibrous material which is drawn in the present process be in intimateassociation with a substantial quantity of water when introduced intothe drawing zone (described hereinafter), i.e., the fibrous material maybe (l) in intimate association with its equilibrium moisture content ofabout 10 to 13 percent by weight based upon the weight of the fibrousmaterial, or (2) be soaking wet and contain up to about 100 percent byweight of water based upon the weight of the fibrous material, e.g.,often about 15 to about 70 percent by weight of water. When the fibrousmaterial is provided in association with an appreciable quantity ofwater the drying may be surprisingly conducted simultaneously withdrawing in the drawing zone (described hereafter) without foaming orsacrifice of tensile properties within the resulting drawn fibrousmaterial. A time consuming separate drying step may accordingly becompletely eliminated.

The polybenzimidazole fibrous material prior to drawing in accordancewith the present process preferably possesses a denier per Ifilament ofabout 1 to 20, and most preferably about 3 to 16 (e.g., 3 to 6 for amultifilament tow and 8 to 16 for a multilament yarn). Multifilamentyarns selected for use in the process preferably contain about 10 to 500filaments, and most preferably about 25 to 200 filaments. Amultifilament tow selected for use in the process preferably containsabout 1,000 to 300,000 filaments, or more, and most preferably about50,000 to 150,000 fil-aments. When tows containing an extremely largenumber of filaments are drawn in accordance with the present invention,it is preferred that the tows be supplied to the drawing zone (describedhereafter) While in a flattened ribbon-like configuration.

THE CONTINUOUS HOT DRAWING The continuous length of polybenzimidazolefibrous material is drawn through the application of a longitudinaltension thereto while passing in the direction of its length for asingle pass through an elongated drawing zone provided with a flowingheated gaseous atmosphere with heat being supplied to the fibrousmaterial both by radiation and convection.

The heated gaseous atmosphere within the elongated drawing zone ismaintained at a temperature of about 400 to 600 C. and, most preferablyat a temperature of about 430 to 530 C. If desired, a temperaturegradient substantially within the above ranges may be selected. It hasbeen found that the present drawing process is not highly dependent uponthe maintenance of a narrowly defined draw temperature for optimumresults as is cornmon with hot shoe polybenzimidazole drawingtechniques.

The desired temperature within the elongated drawing zone is maintainedby radiant heat from the walls of the drawing zone, as well as by thecontinuous introduction of at least one stream of preheated gas into theelongated drawing zone `which impinges upon the moving continuous lengthof polybenzimidazole fibrous material. A heat source may be provided inthe walls of the drawing zone, or heat may be imparted to the walls ofthe drawing zone solely by the stream of preheated gas. For instance, inthe former embodiment variable resistance heating elements may beprovided within the walls of the elongated heating zone, and the streamof gas which is introduced therein preliminarily passed over a similarheating element before entering the same. In order to maintain gas flowwithin the elongated heating zone at least one stream of gas iscontinuously withdrawn from the same. For instance, a stream of gas maybe introduced at the entrance end of the elongated drawing zone, and astream of gas allowed to egress from the exit end of the elongateddrawing zone. Alternatively, -a stream of gas may be introduced at theexit end of the elongated drawing zone and withdrawn from the entranceend of the same. The preheated gas which is introduced into theelongated drawing zone is preferably at a temperature which approximatesthat of the desired temperature of the gaseous atmosphere of the drawingzone at the time of its introduction. The radiant heat which is suppliedto the fibrous material from the walls of the heating zone serves to aidin the maintenance of the flowing gaseous atmosphere of the heating zoneat the desired draw temperature.

The stream of preheated `gas is introduced at a' rate which yields aReynolds number Within the drawing Zone 7 of 50 to 50,000, andpreferably yields a Reynolds number within the drawing zone of 5,000 to10,000.

The nature of the gaseous atmosphere provided in the elongated drawingzone is not critical to the operation of the present process. A gaseousatmosphere is preferably selected, however, which is substantiallyunreactive to the fibrous material passing through the same. Forinstance, air may conveniently serve as the gaseous atmosphere. Inertgaseous atmospheres such as nitrogen, argon, or helium may also beselected, as well as superheated steam, etc.

The draw ratio employed upon a single pass through the elongated drawingzone is about 2:1 to 5:1, and most preferably about 2:1 to 3.5:l.

The term draw ratio, as is well known, is a measure of the degree ofstretching during the orientation of the fibrous material expressed asthe ratio of the cross-sectional area of the undrawn material to that ofthe drawn material. While any of the several known ways for measuring ordetermining draw ratio may be employed, typically the draw ratio isfound by taking the ratio of the surface speed of -a takeup roll at theexit end of the drawing zone to the surface speed of a feed or supplyroll at the entrance end of the drawing zone.

The minimum hot drawing residence time, i.e., the time during which thefiber is heated while suspended in the elongated drawing zone whileunder a longitudinal tension, is dependent upon the single filamentdenier of the fibrous material, the number of filaments in thecontinuous length of fibrous material, and whether the fibrous materialis in a substantially anhydrous form when introduced into the drawingzone. To a limited extent the drawing temperature will also have aneffect as higher draw temperatures will enable the draw to be achievedin slightly shorter residence times. Simple experimentation will enablethe optimum residence times to be obtained. Typically, however, whenfilaments of about 1 to 20 denier are present in a yarn of about l0 to1000 filaments, residence times of about 0.05 to seconds, preferably 0.1to 2 seconds, and more preferably 0.2 to 0.5 seconds are employed. Whenprocessing tows of about 50,000 to 150,000 filaments of l to denier perfilament, typically the residence times are about .05 to seconds,preferably 1 to 15 seconds, and more preferably 3 to 10 seconds. Theshorter residence times are associated primarily with anhydrous fibrousmaterials, smaller denier filaments, and with smaller yarns and tows.

The drawing speed utilized in the present process is at least 10 metersper minute. The drawing speed is defined as the rate at which thecontinuous length of fibrous material is supplied to the elongateddrawing zone while under a longitudinal tension. The drawing speedutilized in the present process is preferably about 10 to 30 meters perminute when drawing a tow, and preferably about to 150 meters per minutewhen processing a multifilament yarn.

The following examples are given as specific illustrations of theinvention. It should be understood, however, that the in-vention is notlimited to the specific details set forth in the examples.

EXAMPLE I A polybenzimidazole yarn, namely, poly-2,2-(mphenylene)5,5'bibenzimidazole was selected as the examplarypolybenzimidazole for -use in carrying out the process of thisinvention.

The polymer was formed into an as-spun yarn in the manner described inthe Example I of U.S. Pat. No. 3,502,756 to Bohrer et al. Moreparticularly, a dope of N,Ndimethylacetamide containing 23 percent byweight of the polymer was extruded through a 50hole jet into a dryspinning chamber containing nitrogen as the drying atmosphere and wasstretched at a draw ratio of 1.06:1 in a steam atmosphere to form a600/50 yarn (50 75 8 filaments making up a yarn having an overall drydenier of 600). l

The yarn was washed with water for 48 hours by batch pressure washing ona bobbin until the residual solvent content was essentially zero. Theyarn was next dried to an essentially zero water content by air ovendrying at C. for 72 hours.

The drawing process for the present invention was next carried outemploying the apparatus of FIG. 1. More specifically, immediately afterdrying, the yarn 1 was withdrawn from a bobbin (not shown) and wascontinuously passed through a tubular elongated drawing zone 2 having alength of four feet while axially suspended therein which was providedwith a flowing heated air atmosphere. The elongated drawing zone 2 had adiameter of 0.825 inch. Situated at each end of the elongated drawingzone 2 were pairs of skewed rolls 4 and 6, and 8 and 10 which maintaineda longitudinal tension upon the yarn while passing through the same. Thedrawing zone 2 was bounded by four draw furnace sections 12, 14, 16 and18, each of which incorporated a variable resistance heater within itswalls. A thermocouple was provided within the elongated drawing zone 2at the center of each draw furnace section, and was connected to gauges20, 22, 24, and 26 from which the temperature of the air atmospherealong the elongated heating zone could be read.

A stream of preheated air was continuously introduced adjacent theentrance end of the drawing zone 2 via inlet 28 at a rate of 700s.c.f.h. with the aid of blower 29. The air was preheated by means ofVariac control 30 connected to resistance heater 32. The stream ofpreheated air within the drawing zone exhibited a Reynolds number of9,900. A yarn finish was continuously applied to the drawn yarn 34 bymeans of transfer roller 36 adjacent the exit end of the elongateddrawing zone 2.

The draw parameters utilized are summarized below:

Draw Drawing zone temperatures speed, C.) meters/ Draw Grams Run min.ratio At 20 At 22 At 24 At 2G tension The single filament propertiesachieved are summarized below:

Tenacity, Denier per grams per Elongation, Run filament denier percentTE 1/2 *TE 1/2=Index of fiber organization wherein T is tenacity atbreak ln grams per denier and E is elongation of percent extension fromoriginal length at break in tensile test. An explanation of this testand its signifilczalceligiven in the Textile Research Journal 36, No. 7,pages 593-602,

EXAMPLE II Example I was repeated with the exceptions indicated. Thepolybenzimidazole yarn was soaking Wet when supplied to the drawing zone2 and contained about 60 percent water by Weight based upon the weightof the yarn. The yarn was simultaneously dried and drawn while passingthrough drawing zone 2.

The draw parameters utilized are summarized below:

Draw Drawing zone temperatures speed, C.) meters] Draw Grams Run rrin.ratio At 20 At 22 At 24 At 26 tension The single ilament propertiesachieved are summarized below:

Tenaeity, grams per denier Elongation, percent EXAMPLE III Drawing zonetemperatures The single ilament properties achieved are summarizedbelow:

Tenacity, grams per denier Denier per Elongaton, lament percent EXAMPLEIV Example III was repeated with the exception that thepolybenzimidazole tow consisted of 2000 filaments having a total denierof 6000.

The draw parameters utilized are summarized below:

Run A Draw speed, meters/min. Draw ratio Drawing zone temperatures, C.:

At 20 At 22 At 24 At 26 Grams tension The single filament propertiesachieved are summerized below:

Run A Denier per filament 1.5 Tenacity, grams per denier 3.9 Elongationpercent 18.8 TE 1/2 17.0

EXAMPLE V 10 'Ihe draw parameters utilized are summarized below:

Run A Draw speed, meters/min. 20 Draw ratio 2:1 Drawing zonetemperatures, C.:

At 26 540 At extensions 518, 540 Grams tension 500 b iIhe single lamentproperties achieved are summarized e ow:

Run A Denier per filament 1.63 Tenacity, grams per denier 5.25Elongation percent 28.1 TE 1/2 27.8

EXAMPLE VI The drawing process of the present invention was carried outemploying the apparatus of FIG. 2. The yarn employed was substantiallyidentical to that described in connection with Examples I-V. The yarn 48had been dried to an essentially zero water content and was withdrawnfrom a bobbin (not shown) and continuously passed through a tubulardrawing zone 50 having a length of 22 inches while axially suspendedtherein which was provided with a flowing heated air atmosphere. Theelongated drawing zone S0 had a diameter of 0.313 inch. Situated at eachend of the elongated drawing zone 50 were pairs of skewed rolls 52 and54, and 56 and 58 which maintained a longitudinal tension upon the yarnwhile passing through the same. Roll 52 was provided at a surfacetemperature of 280 C. by an internal resistance heater. No resistanceheaters were provided in the walls of the heating zone 50.

Air was continuously introduced through line 60 and was fed toflowmeters 62 and 64. The air from owmeter 62 passed over resistanceheater 66 which was actuated by controller 68 after receiving a signalfrom thermocouple 70. The air after passing over resistance heater 66was passed into drawing zone 50 at 72 at a rate of about 75 s.c.f.h. Theair from owmeter 64 passed over resistance heater 74 which was actuatedby controller 76 after receiving a signal from thermocouple 78. The airafter passing over resistance heater 74 was passed into the drawing zone50 at 80 at a rate of about 110 s.c.f.h. via an aspirator nozzledirected toward the exit end 82 of the elongated drawing zone 50.

Approximately percent by volume of the air introduced into the drawingzone at 72 and 80 exited at 82, and about 10 percent by volume of theair introduced into the drawing zone at 72 and 80 exited at 84. Thestream of preheated air produced in the drawing zone 50 exhibited aReynolds number of about 5,400. The preheated gas heated the Walls ofthe drawing zone 50.

' A yarn iinish was continuously applied to the drawn yarn 86 by meansof a transfer roll 88 adjacent the exit end of the elongated drawingzone 50.

The draw parameters utilized are summarized below:

The single lament properties achieved are summarized below:

Draw Drawing zone temperatures sneed, C.) inches from exit end meters]Draw Grams Run min. ratio 0 5 10 15 ?0 tension The single filamentproperties achieved are summarized below:

Tenacity, l Denier per grams per Elongation, Run lament denier percentTE 1/2 For comparative purposes the process of Example VII was repeatedwith the exception that the air flow was cut oi and stagnant heated airwas provided within elongated drawing zone l50. The stagnant air withinthe drawing zone ranged from 450 to 530 C. and was heated solely byradiation from the hot walls of the drawing zone. The yarn passingthrough the drawing zone immediately broke when the air ow wasterminated.

Although the invention has been .described with preferred embodiments,it is to be understood that variations and modications may be resortedto as will be apparent to those skilled in the art. Such variations andmodications are to be considered within the purview and scope of theclaims appended hereto. p

We claim: 1. An improved continuous process for the hot drawing of acontinuous length of a polybenzimidazole brous material containing up toabout 100 percent by weight of water, said drawing occurring withoutfoaming and without employing multiple passes of the -iibrous materialthrough the drawing zone or drawing the fibrous material while incontact with a heated surface, which process comprises:

(a) continuously passing said continuous length of polybenzimidazolefibrous material in the direction of its length, for a single pass,through an elongated drawing zone containing a heated gaseous atmospheremaintained at a temperature of about 400 to 600 C.,

(b) continuously passing a preheated gas into said drawing zone at arate which yields a Reynolds number within the drawing zone of about 50to 50,- 000 so as to contact said iibrous material therein,

Cil

(c) drawing said fibrous material in said drawing zone while in contactwith said preheated gas at a draw ratio of about 2:1 to 5:1 and at adrawing speed of at least 10 meters per minute, and

(d) thereafter continuously withdrawing from said drawing zone a streamof gas and drawn polybenzimidazole brous material.

2. An improved continuous hot drawing process according to claim 1wherein said polybenzimidazole fibrous material consists essentially ofrecurring units of the formula:

/N N\ C/ \R/ N N 1i il wherein R is a tetravalent aromatic nucleus, withthe nitrogen atoms forming the benzimidazole rings upon adjacent carbonatoms of said aromatic nucleus, and R' is selected from the groupconsisting of (1) an aromatic ring, (2) an alkylene group having from 4to 8 carbon atoms, and (3) a heterocyclic ring selected from the groupconsisting of (a) pyridine, (b) pyrazine, (c) furan, (d) quinoline, (e)thiophene, and (f) pyran.

3. An improved continuous hot drawing process according to claim 2wherein said preheated gas is air.

4. An improved continuous hot drawing process according to claim 2wherein said preheated gas is nitrogen.

S. An improved continuous hot drawing process according to claim 2wherein said polybenzimidazole fibrous material contains between about15 and about 70 percent by weight of water.

6. An improved continuous hot drawing process according to claim 5wherein said drawing zone is maintained at a temperature of about 430 to530 C.; wherein said continuous length of polybenzimidazole fibrousmaterial is drawn at a draw ratio of about 2:1 to 35:1; and wherein saidpreheated gas is introduced into said elongated drawing zone at a ratewhich yields a Reynolds number of about 5,000 to 10,000.

7, An improved continuous hot drawing process according to claim 6wherein said preheated gas is air.

8. An improved continuous hot drawing process according to claim 7wherein said polybenzimidazole fibrous material is poly2,2(mphenylene)5,5'bibenzimidazole.

References Cited UNITED STATES PATENTS 3,584,104 6/1971 Bohrer et al.264-205 3,564,835 2/1971 Keefe, Jr. et al. 264--290 N 3,622,660 11/1971Ecker et al. p 264-290 R 3,723,592 3/1973 Bohrer et al. 264-290 R3,541,199 11/1970 Bohrer et al. 264--290 R 3,657,411 4/1972 Bohrer etal. l 264-290 R ROBERT F. WHITE, Rrimary Examiner I. B. LOWE, AssistantExaminer U.S. Cl. X.R. 264-290 R, Dig. 73'

1. AN IMPROVED CONTINUOUS PROCESS FOR THE HOT DRAWING OF A CONTINUOUSLENGTH OF A POLYBENZIMIIDAZOLE FIBROUS MATERIAL CONTAINING UP TO ABOUT100 PERCENT BY WEIGHT OF WATER, SAID DRAWING OCCURING WITHOUT FOAMINGAND WITHOUT WEMPOLYING MULTIPLE PASSES OF THE FIBROUS MATERIAL THROUGHTHE DRAWING ZONE OF DRAWING THE FIBROUS MATERIAL WHILE IN CONTACT WITH AHEATED SURFACE, WHICH PROCESS COMPRISES: (A) CONTINUOUSLY PASSING SAIDCONTINUOUS LENGTH OF POLYBENZIMIDAZOLE FIBROUS MATERIAL IN THE DIRECTIONOF ITS LENGTH, FOR A SINGLE PASS, THROUGH AN ELONGATED DRAWING ZONECONTAINING A HEATED GASEOUS ATMOSPHERE MAINTAINED AT A TEMPERATURE OFABOUT 400 TO 600*C., (B) CONTINUOUSLY PASSING A PREHEATED GAS INTO SAIDDRAWING ZONE AT A RATE WHICH YIELDS A REYNOLD''S NUMBER WITHIN THEDRAWING ZONE OF ABOUT 50 TO 50,000 SO AS TO CONTACT SAID FIBROUSMATERIAL THEREIN, (C) DRAWING SAID FIBROUS MATERIAL IN SAID DRAWINGZONEWHILE IN CONTACT WITH SAID REPHEATED GAS AT A DRAWRATIO OF ABOUT 2:1TO 5:1 AND AT A DRAWING SPEED OF AT LEAST 10 METERS PER MINUTE, AND (D)THEREAFTER CONTINUOUSLY WITHDRAWING FROM SAID DRAWING ZONE A STREAM OFGAS AND DRAWN POLYBENZIMIDAZOLE FIBROUS MATERIAL.